1. Field of Invention
This invention relates to collection and concentration of sunlight for the purpose of reducing the cost of electric power generated from photovoltaic cells.
2. Prior Art
Prior art for concentration of sunlight in photovoltaic systems has employed various techniques using lenses and/or mirrors. In most cases these techniques require two-axis tracking in order to focus the concentrated light on the photovoltaic cells. This increases expense for the tracking mechanism and makes the mounting of panels impractical for many applications such as residential applications that have important aesthetic considerations. Susceptibility to damage and higher maintenance costs are additional disadvantages of two-axis tracking systems. On the other hand solar concentrators that do not require two-axis tracking of the sun suffer from inefficiencies that reduce cost effectiveness. Limitations include reduced concentration factors that affect the photovoltaic cell area savings and suboptimal focusing of light onto surfaces of the photovoltaic cells. Solar concentrators of prior art are also more complex and require good optical tolerances for efficient operation. This increases the cost per unit area of the concentrator. Exceptions are very simple collectors which are relatively less expensive per unit area, but are limited to very low concentration factors and poor focusing of light onto the surfaces of the photovoltaic cells. There are examples of concentrators of this type that do not require any tracking of the sun, but concentration factors are limited to the range of two to three suns and, as a result, savings of photovoltaic cell area are small.
3. Objects and Advantages
Advantages to be sought for solar collectors are high light concentration factors combined with excellent focusing of the concentrated light onto surfaces of the photovoltaic cells. Furthermore, this must be accomplished at low cost of manufacture for the collector. A high concentration factor makes it possible to leverage more electrical energy production from a smaller area of relatively expensive photovoltaic cells. Accurate focusing of light on surfaces of the photovoltaic cells maintains high electrical conversion efficiency over the course of a day taking into account seasonal variations. This invention achieves these advantages by utilizing a cylindrical Cassegrain optical system with planar symmetry. This makes it possible to concentrate the sunlight on a line of photovoltaic cells by rotating the collector to keep the sun in the plane of symmetry. Tracking of the sun can be accomplished simply by rotating the collector through the appropriate angle around its long axis. This enables excellent focusing of sunlight onto surfaces of the photovoltaic cells using a very simple rotation mechanism. Concentration factors can exceed 20× and can be achieved with modest optical quality requirements. This makes it possible to achieve low cost of manufacture for the optical collectors and for the rotation mechanism.